1. Field of the Invention
The present invention is concerned with aseptically operating packing machines and a process for the pre-sterilization thereof. The term xe2x80x9cpacking machinesxe2x80x9d in the present instance, in particular, refers to two types of machines, to wit, on the one hand, machines wherein the web of packing material of suitable thermoplastic plastic or plastic compound foil, by deep drawing, is cyclically fed through the machine, preheated, heated molded by deep-drawing to form containers that are loaded and then sealed by a cover foil, and, on the other hand, machines forming so-called tubular bags wherein the web of packing material is also cyclically molded to form a hose to be longitudinally sealed, with the hose being sealed at the bottom by a transverse seal, then filled and, after withdrawal, closed at the top equally by a transverse seal and then severed from the hose automatically supplied.
2. Description of the Prior State of Art
The package of foodstuffs and semi-luxuries in containers correspondingly molded from webs of packing sheet is required to be in sterile, i.e. substantially aseptical condition. For that purpose, aspetically operating packing machines of the afore-mentioned type are available in the art that have sterile spaces in which are provided the processing or treatment tools for the web of packing foil. In deep-drawing packing machines the processing elements are pre-heating plates, the deep-drawing tools and the filling and sealing elements for the cyclically passing web of packing sheet, while in tubular bag packing machines the said processing elements form the tubular molding and loading stations including the heatable longitudinally sealing tools and all guiding elements for the web of packing sheet located ahead of that station. During operation at a slight excess pressure, sterile air is continuously supplied to the sterile spaces of such machines to maintain the sterile atmosphere clear of re-contamination during operation, insuring that at predetermined points of the sterile spaces the sterile air also can again flow out of the sterile space. After an operational close-down of machines of the afore-described type, be it for shift end reasons or otherwise, it will be necessary to render the aseptic spaces and the afore-mentioned processing tools contained therein again sterile prior to re-putting them into operation.
DE 24 35 037 C2 discloses, for example, a process of pre-sterilizing the surfaces of items wherein the surfaces, prior to supplying hydrogen peroxide (so-called peroxide) as the sterilizing agent, initially, are treated with a flow of water vapor to regularly heat all surfaces to be treated. It is only after such a heating process that peroxide is admixed to the steam, thereby additionally raising the temperature thereof. After having been so pre-sterilized the subsequently introduced peroxide is washed away by non-heated sterile air. As the desired heating of the surfaces, inevitably, involves wetting of the surfaces with condensate containing no sterilizing agent it will have to be left unconsidered to what extent the mixture of sterilizing agent and steam supplied in a second step can take full effect. As, moreover, such sterile spaces and the processing tools contained therein are not clear of corners or gaps, it is unavoidable, that during pre-steaming, such corners or gaps cannot be reached any longer by the peroxide subsequently admixed to the steam because they are quasi already blocked by pure steam condensate, i.e. by water. Apart therefrom this process does not safeguard that the germs protected by the condensate drops are reached by the sterilizing agent at the required concentration because the sterilizing mixture is prevented therefrom due to the condensate already deposited. Another disadvantage resides in that the surfaces to be sterilized are so heated by the steam and by subsequent additional steaming, while adding sterilizing agent, that the mixture of steam/sterilizing agent no longer is safely condensed on all surfaces. The dilemma is that the chemical reactivity of the condensing (i.e. liquid) sterilizing agent, on the one hand, is enhanced, while on the other hand, in view of the destruction of micro-organisms and spores, the chemical reactivity markedly decreases once the sterilizing agent no longer is in liquid form but passes to the gaseous (vaporous) state.
DE 197 26 222 A1 is equally concerned with the question of pre-sterilization especially in connection with a mechanism specifically designed herefore and provided with a so-called reversible blower in order to have gaseous or vaporous sterile agent flow through the sterile spaces along with the tools contained therein in two different directions. Apart from the reversible blower required herefore, this mechanism involves out-of-proportion mechanical efforts, i.e. a large number of conduits and a substantial number of re-switchable valves requiring corresponding valve control means. Moreover, in the afore-described mechanism the sterilizing agent is introduced between two filters involving the danger of that the fine filter coupled to the blower is decomposed. Also, it will have to be left unconsidered how much of the sterilizing agent is retained by the filter or is already chemically reacted in the filter material so that it does not or not in time reach the tunnel or tubing area to be pre-sterilized during the production phase.
A pre-sterilization of a sterile tunnel is also provided with an arrangement according to U.S. Pat. No. 3,820,300, wherein a liquid sterilizing agent is injected into the sterile air supplied prior to commencement of the actual packing processing. After completion of the pre-sterilization, the injection of the sterilizing agent is simply discontinued. The supply of the mixture consisting of sterile air and sterilizing agent as well as the subsequent exclusive supply of sterile air are effectuated in a way similar to DE 197 26 222 A1 via a complex multiplicity of individual nozzles distributed throughout the sterile space, which, individually, are difficult to control and which are connected to so-called xe2x80x9cdistributorsxe2x80x9d. Corners or gaps which are the preferred places, as mentioned before, for bacteria invasions, cannot be reached thereby because the sterile air being the carrier of the injected sterilizing agent has no reason to penetrate such corners or gaps in communication with the atmosphere, let alone that a supplied gaseous sterilizing agent formed of the mixture of sterile air and sterilizing agent has, as mentioned before, a lower sterilizing effect than a condensing (i.e. locally liquid) sterilizing agent.
In the light of the afore-going it is the object of the invention not only to carry out the required pre-sterilization in a satisfactory way but also to minimize the mechanical efforts, using the supply of sterilizing air anyway required for normal package operations as a controllable conveying means for a mixture of steam and sterilizing agent supplied at a mixture ratio predetermined from the very start, insuring at the same time that the said total mixture will find such temperature conditions in the space to be sterilized and on the processing tools contained therein, that, on the one hand, an unimpeded condensation of the mixture of steam and sterilizing agent on all surfaces and in the gaps and crevices be safeguarded and, on the other hand, the temperature-dependent chemical reactivity of the sterilizing agent be optimally secured by a defined temperature regulation.
Proceeding from the traditional practice according to which prior to putting into operation the packing machine concerned, a sterilizing agent, such as hydrogen peroxide or the like, is sprayed into the sterile space and, after the said pre-sterilization, sterile air, during the operative period or during the packing process, is permanently supplied to and discharged from the sterile chamber, the problem involved with the pre-sterilization process according to the invention has been solved by the following process steps:
a) the treatment elements in the sterile chamber which might still be hot, prior to commencing the pre-sterilization process, are brought to a temperature below 120xc2x0 C.;
b) the mixture of water vapor being the carrier medium, and sterilizing agent is effectuated by means of a nozzle to which both components are supplied;
c) the mixture of water vapor and sterilizing agent is introduced at a single point, downstream, directly behind the sterile filter in the same direction as the incoming sterile air serving as the carrier medium, directed toward the sterile chamber;
d) the steam supply to the nozzle is effectuated by a pressure relief valve and a subsequent means regulating the steam volume, whereas the supply of sterilizing agent to the nozzle is from a stock of sterilizing agent held at a constant pressure, and
e) during the pre-sterilizing start-up phase, the supply of sterile air is temporarily discontinued for the generation of a partial return flow of the discharged mixture of water vapor and sterilizing agent, upstream, toward the sterile air filter.
The aseptically operating packing machine still comprises, as it did in the past, a processing track furnished with elements for treating the web of packing foil in a sterile chamber partially open toward the atmosphere and provided with elements for the supply of sterile agent and with a nozzle for a generator of sterile air furnished with blower, heater and sterile filter. In the practice of the invention, a packing machine of the afore-described type, for pre-sterilizing purposes, is furnished with the following:
Downstream, directly behind the sterile air filter, is disposed, within a sterile air passageway terminating in the sterile chamber, a mixing nozzle connected to conduits for feeding steam and sterilizing agent, which is arranged toward the direction of the termination of the sterile air passageway in the sterile chamber, with a tank allocating the sterilizing agent held at a constant pressure and provided with a pressure relief valve disposed ahead thereof being disposed in the sterilizing agent supply line, and a pressure relief valve including means for regulating the steam volume being provided in the steam supply conduit.
In the light of the afore-going, the invention is not restricted to the simple feature of reducin a multiplicity of spraying ports according to DE 197 26 222 A1 and U.S. Pat. No. 3,820,300 to one single port, as this measure alone would not achieve a satisfactory pre-sterilization of the entire sterile chamber; the afore-mentioned additional process features and objects will be necessary, as on the one hand, a special arrangement (utilization of the sterile air flow) and a directional orientation of the mixing nozzle have proved to be necessary and, on the other hand, a mixing ratio of steam and sterilizing agent insuring a satisfactory germ destruction will have to be taken into consideration. In addition, due to the arrangement of the mixing nozzle directly downstream behind the sterilizing air filter, the latter is most easily and controllably incorporated into the pre-sterilizing process in that the sterile air blower is simply turned off for a short period of time. Moreover, the feature of the temperature decrease of the elements of treatment insures that the subsequently introduced mixture of sterilizing agent can condense throughout the place, including all corners and gaps without being affected by moisture otherwise already contained therein. Preferably and with advantage, the temperature is decreased to a value below the condensation temperature of the mixture of steam and sterilizing agent.